It is desirable to control the drive train torque of a machine while the machine is dozing or digging. For example, in an earth working type machine, an operator typically "inches" the machine when working material while providing full power to the implement hydraulics to capture the material. It is important to control the amount of drive train torque to reduce rimpull, which is useful for reducing slipping.
In one conventional method of inching, the transmission is kept in gear and the brakes are manually modulated by use of a foot pedal. In another conventional method of inching, an impeller clutch is connected between a machine's engine and transmission. Typically, the impeller clutch is actuated through an operator pedal. The operator pedal acts to engage and disengage the impeller clutch; thereby, varying the power transmitted by the drive train to slow the machine.
However, the prior art methods of controlling the machine to reduce drive train torque, reduce slipping and prevent engine stalling are largely undesirable because it requires considerable operator effort. Typically, three operator pedals are needed, one to control the engine acceleration, one to control clutch pressure, and yet another to control machine braking. What is needed is an electrohydraulic control device that regulates the amount of drive train torque and prevents engine stall while being easily manipulated by the operator.
The present invention is directed to overcoming one or more of the problems as set forth above.